Anyway I hardly agree that Slaugher is only DPS focused, my main is Healer, but I try to join always as DPS because of the nature of the fight.

As someone suggested I hope they change how roles get Battle High/Fever but I have 2 options:

1. The Healers and Tanks get buff that enhance their main role (Damage reduction, HP for tanks and Healing potency and MP or Spellspeed for healers)

2. The Healers and the tanks get a massive DPS advantages (like doubling the INT of healer or halving the tanks "recast time" of their skills), and to be hones I prefere it, so even them can take part in the slaughter mode in the slaughter way

In any case how they get Battle high or battle fever should be adjusted.
For healers for example it could be fine if they have to reach a threshold of HP healed (overheal didn't take part of the count), once reached they gain Battle high/ fever.
For tanks... I don't know :/
Maybe lowering to 3 and 6 the threshould for battle high/fever?